The present invention relates to an apparatus for collecting chemical samples, and more specifically, to an apparatus for accumulating a concentration of chemicals over a period of time.
To prevent injury resulting from exposure to toxic chemicals, the presence of toxic chemicals must be detected while their concentrations are below toxic levels. Accordingly, to detect highly toxic chemicals, devices capable of detecting low concentrations within a short period of time are needed.
One prior art device for detecting low concentrations of chemicals includes a pump such as a diaphragm pump and a preconcentrator tube. The pump pumps air through a preconcentrator tube where the chemicals accumulate. The preconcentrator tube may comprise a low thermal mass tube that houses a sorbent material. The terms xe2x80x9cpreconcentrator tubexe2x80x9d and xe2x80x9csorbent materialxe2x80x9d are well known in the art and correspond to a tube for accumulating chemicals and a material for sorbing (and, therefore, accumulating the chemicals), respectively.
A heating element wrapped around the preconcentrator tube is used to heat the sorbent material and thereby desorb the chemicals. A single pump is used to pump air through the preconcentrator tube and to a detector. Chemicals in the air accumulate in the sorbent material contained within the preconcentrator tube. The heater on the outside of the preconcentrator tube is activated, and chemicals adsorbed onto the sorbent material are released. The chemicals released from the sorbent material are entrained in the air being pumped to the detector.
This prior art configuration is simple and low cost. Additionally, this configuration consumes little power in comparison to other prior art designs. However, one drawback of this prior art configuration is that the detector is unable to measure chemicals contained in the air in real-time since a period of time is required to accumulate chemicals in the sorbent material. During the period of time while the chemicals are accumulating within the preconcentrator tube, the user is blind to the presence of toxic chemicals in the air. This period of time may last several minutes. During this time, the user will be exposed to the chemicals, which may be present in toxic levels. Only when heat is applied to the sorbent material are the chemicals released and detected.
Another disadvantage of this prior art design is that the desorbed chemical must be passed through the entire length of the sorbent material prior to reaching the detector. However, the chemical may react with the sorbent material as it is passed through it. Consequently, a sample of chemical traversing the sorbent material may not accurately reflect the concentration of chemical entering the sorbent material. Additionally, unless the preconcentrator tube is heated for a sufficiently long enough time, all of the chemicals accumulated in the sorbent material will not be released. Again, the sample of chemical released from the sorbent material that reaches the detector may not accurately reflect the concentration of chemical entering the sorbent material. Additionally, the device may exhibit a memory effect in which chemicals remaining in the sorbent material may be released when the preconcentrator tube is heated a subsequent time. Artificially higher levels of chemical may be produced at the detector during this subsequent heating.
Another prior art configuration employs two pumps, a first pump and a second pump, a three-port three-way valve, a preconcentrator tube, and a detector. With the three-port three-way valve in the first position, two separate paths are created. A first path extends from the first inlet to the preconcentrator tube and from the preconcentrator tube to the first pump. A second path extends from the second inlet to the detector and from the detector to the second pump. In a second position, the three-port three-way valve creates a flow path from the second inlet to the preconcentrator tube, from the preconcentrator tube to the detector, and from the detector to the second pump.
With the three-port three-way valve in the first position, air is drawn in the first inlet, pumped through the three-port three-way valve and through the preconcentrator tube, and pumped out an exhaust connected to the first pump. In this manner, chemicals are collected in sorbent material contained inside the preconcentrator tube. Simultaneously, chemicals are drawn from the second inlet through the valve and to the detector. Thus, real-time detection is provided for chemicals present at concentrations high enough to be sensed by the detector.
The first pump is subsequently turned off, the three-port three-way valve is switched to the second position, and a heater surrounding the preconcentrator tube is activated. With the heater activated, the chemicals collected in the sorbent material will be released and drawn into the detector by the second pump.
When the three-port three-way valve is in the second position, the direction that the air is pumped through the preconcentrator tube is reversed. Accordingly, all of the chemicals collected in the sorbent material do not have to travel through the sorbent material to reach the detector, thus, lowering the likelihood of a chemical reaction between the chemicals and the sorbent material. Desorption is also more efficient. The sorbent material does not need to be heated as long since the chemical does not have to pass through all the sorbent material. Despite these advantages, this prior art configuration has serious disadvantages. In particular, the three-port three-way valve is large in volume and requires large amounts of energy such that its use in portable chemical sensor systems is impractical.
A further prior art configuration substitutes the three-port three-way valve employed in the second prior art configuration with three single-port three-way valves that are magnetically latched and consume less power than non-magnetically latched valves. Overall power consumption can be reduced by switching to magnetically latched valves. Although the size of three single-port three-way valves is slightly larger than the size of a single three-port three-way valve, the number of batteries required for the three single-port three-way valves is less. Nevertheless, this configuration requires too much space and energy for many field applications.
Accordingly, there is a need in the art for a chemical detection apparatus that may be miniaturized, is lightweight, and has relatively low power consumption.
According to one aspect of the invention, an apparatus for detecting one or more chemicals comprises a sorbent element for sorbing the one or more chemicals, a bi-directional pump, and at least one chemical detector. The sorbent element has a fluid flow path therethrough. The bi-directional pump is connected to pump fluid through the fluid flow path of the sorbent element in a first direction during sorption of the one or more chemicals and to pump fluid through the fluid flow path of the sorbent element in a second direction during desorbtion of the one or more chemicals. The at least one chemical detector is connected to receive desorbed chemicals. The apparatus may further comprise an enclosed passageway from the bi-directional pump to the sorbent element and from the sorbent element to the chemical detector. The sorbent element may comprise a tube having a sorbent material therein.
In another aspect of the invention, an apparatus for detecting one or more chemicals comprises a sorbent element having an inlet and an outlet, a bi-directional pump, and a detector comprising a detector housing containing at least one chemical sensor. The sorbent element comprises a sorbent material. The bi-directional pump has an intake and a vent. The bi-directional pump is adapted to pump fluid from the intake to the vent when pumping in a first direction and to pump the fluid from the vent to the intake when pumping in a second direction. The outlet of the sorbent element is connected to the intake of the bi-directional pump such that the fluid flows from the sorbent material to the bi-directional pump when the pump is pumping in the first direction. The inlet of the sorbent element is connected to the detector such that fluid flows from the bi-directional pump to the sensor when the pump is pumping in the second direction. The sorbent element may comprise a porous polymer comprising 2,6 diphenyl-xcfx81-phenylene oxide. The apparatus may further comprise a detector pump having an intake and a vent, wherein the intake of the detector pump is connected to the detector containing the sensor.
Yet another aspect of the invention comprises a method of detecting one or more chemicals contained in a fluid. This method comprises providing a plurality of flow paths including a first flow path for fluid flow through a sorbent element and a second flow path for fluid flow to at least one chemical detector. The first and second flow paths are connected to respective first and second pumps. The fluid containing the one or more chemicals is inputted into an inlet. A first portion of the fluid containing the one or more chemicals is flowed from the inlet through the first flow path. At least a portion of the one or more chemicals are thereby collected within the sorbent element. A second portion of the fluid containing the one or more chemicals is simultaneously flowed from the inlet through the second flow path to the chemical detector. Fluid is flowed through both of the first and second flow paths without altering the connection of the flow paths with the pumps to deliver the one or more chemicals collected in the sorbent element to the chemical detector. The method may further comprise heating the sorbent element to desorb the one or more chemicals collected in the sorbent element.